The invention relates to a brush seal for use in a gas turbine engine.
Brush seals are used to seal shafts and other rotating components of gas turbine engines. Such seals generally include a bundle of densely packed bristles sandwiched between two plates. The bristles typically extend from a stationary housing, with free ends of the bristles wiping against a surface of the shaft or other rotating component to provide a seal thereagainst.
It is desirable that the bristles of the brush seal are relatively flexible, so that they may move radially to accommodate shaft excursions. Therefore, the bristles are usually mounted such that they are oriented at an angle to the radial direction of the rotating component. This allows the bristle to deflect radially outwardly if the rotating component expands or perhaps rotates unevenly. However, a problem with the bristles lying at an angle to the radial direction is that aerodynamic forces tend to force the bristles inwardly against the rotating component (this being termed xe2x80x9caerodynamic blow-downxe2x80x9d). The greater the angle of the bristles to the radial direction, the stronger the inward force. Because the bristles are forced against the rotating component, this causes wear of the bristles.
The general trend in development of brush seals is to have the seals aligned close to the radial direction of the rotating component, this resulting in bristles which are stiffer against expansion or uneven rotation of the rotating component but which are less subject to aerodynamic blow-down. This causes rapid wear during excursions/growth of the rotating component.
According to the invention there is provided a brush seal for sealing between first and second components of a gas turbine engine, the brush seal including a housing and a plurality of flexible bristles held within the housing so as to protrude therefrom, a free end of each bristle being adapted to contact and seal against a seal surface of the first component; characterised in that the brush seal further includes a stop member for limiting movement of the free ends of the bristles towards the seal surface of the first component.
Preferably the stop member includes means for varying its distance from a part of the housing which holds the bristles. Preferably the stop member includes means for varying this distance in dependence upon the temperature of the stop member. The stop member may include means for inducing a part of the stop member to bend by varying amounts depending upon its temperature. The stop member may include a bi-metallic strip.
Preferably the first component is a rotor and the second component is a stator. Preferably the housing includes a generally annular member which surrounds a generally cylindrical part of the rotor and is spaced therefrom. Preferably the free ends of the bristles are adapted to seal against an outer surface of the rotor.
The stop member may be mounted on or formed as part of the housing, the stop member being located radially inwardly of the part of the housing which holds the bristles. The term xe2x80x98radialxe2x80x99 refers to the radial direction of the rotor.
The stop member includes a generally cylindrical member which may be connected to the housing by a generally radial member. The stop member may include a support ring located at a distal edge of the generally cylindrical member, the support ring being in contact with the bristles. The support ring may exert a radially outward force on the bristles and the magnitude of the force may vary depending upon the temperature of the stop member.
Each bristle may include a shaft portion and a seal portion, the shaft portion and the seal portion each being substantially straight but being angled to one another. An end of the shaft portion is preferably held within the housing and an end of the seal portion is preferably in contact with the seal surface of the first component. The stop member preferably contacts the bristle in a region where the shaft portion and the seal portion join. The angle between the shaft portion and the seal portion of each bristle may be between 110xc2x0 and about 140xc2x0. The seal portion is preferably oriented substantially radially in relation to the rotor in use.
According to the invention there is further provided a gas turbine engine including a brush seal as defined in any of the preceding six paragraphs.